The invention relates to methods for treating asbestos containing materials for removing it from substrates and for converting the asbestos therein to a nonasbestos material.
Asbestos is a commercial term applied to a group of silicate minerals which occur in fibrous form. There are six principal asbestos minerals. Of these six minerals, only one, chrysotile asbestos, belongs to the group classified as serpentine asbestos, that is, minerals characterized by long fibers that are serpentine in shape. The chemical composition of chrysotile asbestos may be represented as: Mg.sub.3 (Si.sub.2 O.sub.5)(OH).sub.4 or 3MgO.2SiO.sub.2.H.sub.2 O. The crystalline structure of chrysotile asbestos consists of alternating layers of silica and magnesium oxide/hydroxide bound to each other through covalently shared oxygen. These layers are transverse to the fiber axis.
The other varieties of asbestos are silicates of magnesium, iron, calcium, and sodium. These varieties of asbestos belong to the amphibole (straight fiber) group of minerals. About 95% of world production is the chrysotile form of asbestos.
Due to the unique properties of the asbestos minerals, many different kinds of products were developed during the 1940's through the early 1970's that incorporated asbestos fibers for fire resistance, moisture control, and thermal insulation. Many building products, for example, friable thermal insulation, asbestos-cement pipe, asbestos-cement sheet, floor and roof shingles, transite tiles, acoustical plaster, insulation and fire-retardant paper products, and high-temperature insulation, include asbestos fibers. In the overwhelming majority of cases, these products contain the chrysotile form of asbestos.
For a number of years now it has been recognized that many chronic diseases are associated with the inhalation of airborne asbestos fibers. These diseases include lung cancer, chronic fibrosis of the lung lining, and mesothelioma (a rare but fatal cancer of the lungs). Although not completely understood, it is believed that when an asbestos fiber comes into contact with a living cell, the asbestos fiber irritates the cell lining and leads to its eventual weakening. After such weakening, it is believed the asbestos fiber enters the cell. Once inside the living cell, the asbestos fiber appears to set in motion a collagen synthesis ultimately resulting in chronic fibrosis and a potential for developing carcinoma.
Due to its hazardous nature, there has been a concerted effort by governmental agencies to ban the use and encourage the removal of materials containing asbestos fibers. The U.S. Environmental Protection Agency has set an upper limit of 1% for the allowable asbestos fiber content in building materials. Furthermore, local governmental agencies in many cities, for example, New York City, require the removal of asbestos materials from buildings before they will issue permits for building renovation or demolition. Many safeguards must be employed to prevent inhalation of airborne asbestos fibers by workers and others in the vicinity of the work area. Respirators must be worn by workers handling the asbestos. Any area in a building in which asbestos material is exposed or is being removed must be isolated by partitions from the remainder of the building. Also, the work area must be kept at a negative pressure with respect to the atmosphere to prevent airborne fibers from leaving the area. Needless to say, these measures are both cumbersome and costly. Additionally, disposal of asbestos products removed from the building also remains a problem.
A number of methods have been proposed for rendering asbestos less harmful but without substantially affecting its significant physical and chemical properties. In U.S. Pat. No. 4,401,636 (Flowers) a method is described for treating silicate minerals with an aqueous metal salt solution to form a metal-micelle silicate. The method purports to render the resulting silicate less harmful to living cells while the treated silicate retains most of its asbestos-like properties. However, the method proposed therein is not totally satisfactory since it does not destroy the fibrous nature of the asbestos. According to the method described in U.S. Pat. No. 4,401,636, a metal is added to the crystal structure of the asbestos, thereby forming a metal-micelle which masks the iron-binding sites in the asbestos. According to that patent, the metal-micelle asbestos, when introduced into a living cell, does not react with cellular iron. Therefore, it is asserted, the reaction that is believed to initiate fibrosis should be blocked and biological hazards associated with exposure of living organisms to asbestos should be reduced.
Accordingly, it is an object of the present invention to provide a process for removing asbestos-containing materials from substrates which is simple and less expensive than present methods.